JPH0644624A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To enhance sensitivity by forming a reproducing layer and a recording layer with films of amorphous alloys represented by specified general formulae, respectively, and making the Co content of the reproducing layer higher than that of the recording layer. CONSTITUTION:This magneto-optical recording medium has a reproducing layer 3 made of a film of an amorphous alloy represented by a general formula (TexDy1-x)z(FeyCo1-y)1-z (where 0.3<=x<=0.5, 0.80<=y<=0.85 and 0.15<=z<=0.19) and a recording layer 4 made of a film of an amorphous alloy represented by a general formula (TlxDy1-x)z(FeyCo1-y)1-z (where 0.3<=x<=0.5, 0.88<=y<=0.93 and 0.20<Z<=0.25). The Co content of the reproducing layer 3 is higher than that of the recording layer 4. Sensitivity is further enhanced and this recording medium well deal with the increase of the capacity of a file and the increase of the rate of transmission.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium such as a magneto-optical disk for recording, reproducing and erasing information by using laser light.

[0002]

2. Description of the Related Art A magneto-optical recording medium such as a magneto-optical disk has a large storage capacity like a conventional optical disk because information is recorded, reproduced and erased by using a laser beam, and a magnetic material is used for a recording layer. Therefore, it can be rewritten. In addition, recording and reproducing can be performed in a non-contact manner, and the influence of dust can be avoided, so that the reliability is excellent. As a material used for the recording layer, a rare earth-transition metal (RE-TM) amorphous alloy is presently in the mainstream because it has no grain boundary noise and is easily formed into a perpendicular magnetization film by using sputtering.

On the other hand, a file system using a magneto-optical disk will have a larger capacity and a higher transfer rate in the future, so that the recording layer has a Kerr rotation angle (θ) that influences C / N.
It is required that the material has a large k), a low Curie temperature (Tc) that affects recording sensitivity, and a large coercive force (Hc) for stabilizing the bit size (magnetic domain) of 1 μm or less. However, since there is no RE-TM amorphous alloy that satisfies all the conditions at the same time, it is the current practice to combine RE-TM amorphous alloys with different properties into a multilayer film structure. is there.

A magneto-optical recording medium having a magnetic film having such a multilayer film structure is called an exchange coupling type magneto-optical recording medium. Among them, in the two-layer film type medium, the reproducing layer and the recording layer are separately provided, and the Curie temperature (Tc) is set in the reproducing layer.
Is high, the coercive force (Hc) is small, and the Kerr rotation angle (θ
A material having a large k) is used, and a material having a low Curie temperature (Tc) and a large coercive force (Hc) is used for the recording layer. In such a structure, conventionally, GdFe, GdFeCo, Bi-substituted YIG or the like is used for the reproducing layer, and TbFe, TbFeCo or the like is used for the recording layer.

[0005]

However, even a two-layer type magnetic film using these materials cannot be said to be sufficiently compatible with a large capacity and a high transfer rate, and a higher sensitivity and higher There has been a demand for realization of a C / N magneto-optical recording medium.

The present invention has been made in view of the actual situation of the prior art as described above, and further improves the sensitivity and the C / N ratio.
It is an object of the present invention to provide an improved magneto-optical recording medium.

[0007]

In order to achieve the above object, according to the present invention, a magneto-optical recording medium in which at least an interference layer, a reproducing layer, a recording layer and a protective layer are laminated in this order on a substrate. In the above, the reproducing layer and the recording layer are made of amorphous alloy films represented by the following general formulas 1 and 2, respectively, and the Co composition in the reproducing layer is C in the recording layer.
Provided is a magneto-optical recording medium having a larger O composition.

[Chemical 1] (However, 0.3 ≦ x ≦ 0.5, 0.80 ≦ y ≦ 0.8
5, 0.15 <z ≦ 0.19)

[Chemical 2] (However, 0.3 ≦ x ≦ 0.5, 0.88 ≦ y ≦ 0.9
According to the present invention, the thickness of the reproducing layer is smaller than that of the recording layer and is 200 Å or less. A recording medium is provided.

The structure of the magneto-optical recording medium of the present invention will be described below with reference to FIG. FIG. 1 is a cross-sectional view schematically showing an example of the structure of the magneto-optical recording medium according to the present invention. An interference layer (protective layer) 2, a reproducing layer 3, a recording layer 4, a protective layer 5 are formed on a transparent substrate 1 with pregrooves. And the reflective layer 6 are sequentially laminated.

The substrate 1 is made of polycarbonate (PC),
A grooved molded substrate made of a resin such as polymethylmethacrylate (PMMA) or amorphous polyolefin (APO) is used, but is not limited thereto. The substrate shape is preferably a disk shape, and the thickness is usually 0.6 to 1.2 mm.
It is a degree.

The interference layer (protective layer) 2 is provided between the substrate 1 and the reproducing layer 3 and recording layer 4. A transparent material having a high refractive index (preferably 2.0 or more) is used for the interference layer 2,
The purpose is to increase the apparent Kerr rotation angle by utilizing the multiple reflection of the reproduction light in this layer, thereby raising the carrier level and improving the C / N. Furthermore, it is necessary to have a role as a protective layer that prevents corrosion of the RE-TM amorphous alloy used for the reproducing layer 3 and the recording layer 4 due to selective oxidation (oxidation of RE). Therefore, the interference layer 2
The preferred materials used for are SiO ₂ , Ta ₂ O
₅ , Al ₂ O ₃ —Ta ₂ O ₅ , SiN, SiON, SiBO
N etc. can be mentioned. Film thickness is 500-2000
Å, preferably 800 to 1200Å.

The feature of the present invention lies in the reproducing layer 3 and the recording layer 4. Both layers are made of a TbDyFeCo amorphous alloy, but the ratio of each element is different in order to give the reproducing layer 3 and the recording layer 4 different characteristics. That is, the reproducing layer 3 and the recording layer 4 have the compositions represented by the following general formulas 1 and 2, respectively, and the C in the reproducing layer 3 is
The o composition is set to be larger than the Co composition in the recording layer 4.

[Chemical 1] (However, 0.3 ≦ x ≦ 0.5, 0.80 ≦ y ≦ 0.8
5, 0.15 <z ≦ 0.19)

[Chemical 2] (However, 0.3 ≦ x ≦ 0.5, 0.88 ≦ y ≦ 0.9
3, 0.20 <z ≦ 0.25)

TbDyFeCo is currently the mainstream TbFeC
The sensitivity is higher than that of o, and the Curie temperature (Tc), coercive force (Hc) and the like can be freely controlled by adjusting the content of each element. Above all, the Dy amount is reflected on the Curie temperature (Tc), and if the Dy amount is increased relative to the Tb amount, the Curie temperature (Tc) can be lowered to around 130 ° C. Further, the Co amount is reflected on the Kerr rotation angle (θk), and the Kerr rotation angle increases as the Co amount increases. However, as the Co content increases, the Curie temperature (Tc) increases, and the sensitivity decreases.

On the other hand, for high sensitivity and high C / N, the Kerr rotation angle (θk) of the reproducing layer 3 is preferably as large as 0.4 ° or more, and the coercive force (Hc) is 1 to 6 KOe.
It is preferable that the recording layer 4 is the same as or smaller than the recording layer 4, and the Curie temperature (Tc) is preferably 230 to 300 ° C. The Curie temperature (Tc) of the recording layer 4 is 200.
It is preferable that the temperature is as low as ° C or less and the coercive force (Hc) is as large as 10 KOe or more.

These conditions are R of the reproducing layer 3 and the recording layer 4.
This can be satisfied by defining the composition of the E-TM amorphous alloy as shown in the above general formulas 1 and 2. Particularly, in order to obtain a large Kerr rotation angle (θk) in the reproducing layer 3, the Co composition of the reproducing layer 3 is larger than that of the recording layer 4, and the film thickness of the reproducing layer 3 is smaller than that of the recording layer 4. Is desirable. The extent to which the thickness of the reproducing layer 3 is reduced is the recording layer 4
1/2 or less is preferable. When the film thickness of the reproducing layer 3 is larger than half the film thickness of the recording layer 4, the Curie temperature (Tc) of the reproducing layer 3 is higher, so that recording is difficult to be formed and high sensitivity is hindered. Further, since the Kerr rotation angle (θk) is an effect of reflected light, it is not necessary to make the thickness of the reproducing layer 3 too thick, and conversely, if it is made extremely thin, the magnetization may be inclined in-plane due to a self-demagnetizing field. Therefore, some thickness is required. Therefore, the thickness of the reproducing layer 3 is preferably 50 to 200Å, the thickness of the recording layer 4 is preferably 150 to 250Å, and the ratio of the reproducing layer 3 to the recording layer 4 is preferably 1: 2 or less. .

The protective layer 5 is provided in order to prevent the reproduction layer 3 and the recording layer 4 from being corroded by moisture from the air and to prevent them from being mechanically damaged. As the material of the protective layer 5, the same material as the interference layer 2 can be used, but other materials can also be used. If the film thickness of the protective layer 5 is too thick, it also has a great influence on the improvement of recording sensitivity, so that it is preferably 600 Å or less.

In the case of a reflective film type medium, the reflective layer 6 is provided on the protective layer 5. When the reflection layer 6 is provided, when light is incident from the substrate surface side and the Kerr rotation angle (θk) is read out as a signal, the signal read from the reproduction layer 3, that is, the Kerr rotation angle (θk) signal, A signal that has passed through the recording layer 4 and rotated by Faraday overlaps with each other, and the apparent rotation angle can be increased. As the material of the reflective layer 6, Al, Ni, Cr, Mo, Pt, Au, etc., or alloys thereof can be used. The film thickness is 3
A value of 00 to 1000Å is suitable.

Means for forming the interference layer 2, the reproducing layer 3, the recording layer 4, the protective layer 5, and the reflective layer 6 include physical vapor deposition methods such as sputtering and ion plating, and plasma C.
A chemical vapor deposition method such as VD is used.

In addition to the layer structure shown in FIG. 1, the reflective layer 6 is not provided, an organic protective film (cover layer) having a thickness of 5 to 10 μm is provided on the reflective layer 6, and a pair of media. It is possible to have an appropriate structure such as a structure in which the above is bonded with an adhesive.

[0019]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples.

Examples 1 to 5 A polycarbonate substrate with a pre-groove having a diameter of 130 mm and a thickness of 1.2 mm was placed in a vacuum chamber of a sputtering apparatus, and the chamber was evacuated to a pressure of 5 × 10 ⁻⁷ torr or less. Then, a mixed gas of Ar and N ₂ was introduced into the vacuum chamber, the pressure was adjusted to 3 × 10 ⁻³ torr, and a Si target was used to form an SiN film as an interference layer on the substrate by an rf magnetron sputtering device with a power of 2 kW. Then, a reproducing layer and a recording layer were sequentially formed to have a thickness shown in Table 1 by a DC magnetron sputtering method using a TbDyFeCo alloy target having a composition shown in Table 1. Then, a SiN film having a thickness of 300 Å is formed as a protective layer on it by the same method as that for forming an interference layer, and then a DC magnetron sputtering method is further performed using an AlTi (Ti: 1 atm%) alloy target. The reflective layer to 45
It was formed to a thickness of 0Å. Finally, an organic protective film (trade name: SD301; manufactured by Dainippon Ink and Chemicals, Inc.) having a thickness of 4 μm was formed on the reflective layer to obtain a magneto-optical recording medium according to the present invention.

Comparative Examples 1 and 2 A magneto-optical recording medium was prepared in the same manner as in the above examples except that the reproducing layer was not provided and the recording layer composition and film thickness were as shown in Table 1, and comparison was made. As an example.

The thickness, composition, coercive force (Hc), Curie temperature (Tc), Kerr rotation angle (θk) of the reproducing layer and the recording layer in the magneto-optical recording medium manufactured in the above-mentioned Examples and Comparative Examples.
Is shown in Table 1.

[0023]

[Table 1]

The C / N and recording sensitivity of the magneto-optical recording media of the above Examples and Comparative Examples were evaluated under the following recording / reproducing conditions. The results are also shown in Table 1. (Recording / reproducing conditions) -Recording radius 30 mm-Recording frequency 6.1 MHz (pulse width 36
nsec) ・ Disk rotation speed 3000 rpm ・ Recording / erasing magnetic field −200 Oe / 250 Oe ・ Laser wavelength 780 nm ・ Recording laser power 3 to 12 mW ・ Reproducing laser power 1.5 mW

From Table 1, the medium of the example has a larger Kerr rotation angle (θk) than the medium of the comparative example, and
It was confirmed that high C / N and high sensitivity could be achieved.

According to the present invention, in a two-layer film type magneto-optical recording medium provided with an interference layer and a reproducing layer, the reproducing layer and the recording layer have a specific composition and the Co composition in the reproducing layer is Co. Since an amorphous alloy having a larger composition is used, higher sensitivity and higher sensitivity can be achieved, and a magneto-optical recording medium that can sufficiently cope with a large file capacity and a high transfer rate can be provided. It will be possible.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing a configuration example of a magneto-optical recording medium according to the present invention.

[Explanation of symbols]

 1 substrate 2 interference layer (protective layer) 3 reproducing layer 4 recording layer 5 protective layer 6 reflective layer

Claims (2)

[Claims] 1. In a magneto-optical recording medium in which at least an interference layer, a reproducing layer, a recording layer and a protective layer are laminated in this order on a substrate, the reproducing layer and the recording layer are each represented by the following general formula 1
2. A magneto-optical recording medium comprising an amorphous alloy film represented by Chemical Formula 2 and having a Co composition in the reproducing layer higher than that in the recording layer. [Chemical 1] (However, 0.3 ≦ x ≦ 0.5, 0.80 ≦ y ≦ 0.8
5, 0.15 <z ≦ 0.19) (However, 0.3 ≦ x ≦ 0.5, 0.88 ≦ y ≦ 0.9
3, 0.20 <z ≦ 0.25) 2. The magneto-optical recording medium according to claim 1, wherein the thickness of the reproducing layer is smaller than that of the recording layer and is 200 Å or less.